1. Field of the Invention
The present invention relates to a thin film magnetic head in general employed in a magnetic recording medium drive or storage device such as a magnetic disk drive and a magnetic tape drive, for example.
2. Description of the Prior Art
A non-magnetic gap layer is interposed between an upper and a lower magnetic pole layer in a thin film magnetic head. The non-magnetic gap layer is designed to extend to the central position of a swirly conductive coil pattern from the front end exposed at a medium-opposed surface or bottom surface of a head slider. As conventionally known, the non-magnetic gap layer maintains its thickness constant in a range in general referred to as a gap depth. Reduction in the gap depth is supposed to lead to enhancement of a magnetic field leaked out of the medium-opposed surface, namely, a magnetic field for recordation. As disclosed in Japanese Patent Application Laid-open No. 11-149621, for example, an insulation layer can be utilized to define the rear end of a region determined by the gap depth. The insulation layer in this case is designed to swell from the surface of the lower magnetic pole layer at a position retracted from the medium-opposed surface.
A thin film magnetic head is well known to include a tip pole piece connected to an upper magnetic pole layer. In general, the tip pole piece is subjected to a flattening polishing treatment prior to formation of the thin film swirly coil pattern. When the tip pole piece is flattened in this manner, a thinner film portion is generated in the tip pole piece right on the aforementioned insulation layer swelling from the surface of the lower magnetic pole layer. A magnetic flux is introduced to the front end of the tip pole piece after having passed through the thinner film portion. The magnetic flux thus reaching the front end of the tip pole piece is allowed to leak out of the medium-opposed surface so as to form a magnetic field for recordation.
It has been revealed that a reduction in the gap depth of the aforementioned type of the tip pole piece leads to reduction in the magnetic field for recordation. In particular, the tip pole piece made of a thinner layer tends to suffer from a remarkable reduction in the magnetic field for recordation if the gap depth is reduced in the aforementioned manner. On the other hand, if the tip pole piece gets thinner, it is possible to form or shape the tip pole piece at a higher dimensional accuracy. Specifically, the core width of the tip pole piece can be reduced in a relatively facilitated manner.
It is accordingly an object of the present invention to provide a thin film magnetic head capable of establishing a larger magnetic field for recordation even when the upper surface of the upper magnetic pole is subjected to a flattening treatment.
According to a first aspect of the present invention, there is provided a thin film magnetic head comprising: a lower magnetic pole extending rearward from a front end exposed at a medium-opposed surface and defining a flat upper surface; a non-magnetic auxiliary layer designed to swell from the flat upper surface of the lower magnetic pole at a position retracted from the medium-opposed surface; a non-magnetic gap layer extending over the flat upper surface of the lower magnetic pole by a constant thickness at least in a range between the medium-opposed surface and the non-magnetic auxiliary layer; and an upper magnetic pole extending over the non-magnetic gap layer by a predetermined thickness at least in a range defined as a gap depth, said upper magnetic pole defining a thinner film portion of a reduced thickness smaller than the predetermined thickness on the non-magnetic auxiliary layer, wherein a neck height of the upper magnetic pole is set smaller than the gap depth.
The core width of the upper magnetic pole starts getting larger or wider in the lateral direction at the position determined by the neck height. The neck height smaller than the gap depth serves to establish a reduction in the thickness of the upper magnetic pole in a range rearward of the position determined by the neck height. The upper magnetic pole is allowed to suffer from less magnetic saturation at the thinner film portion as compared with the case where the neck height is set larger than the gap depth. A sufficient quantity of a magnetic flux can be introduced into the front end of the upper magnetic pole through the thinner film portion. It is possible to reliably enhance a magnetic field leaked out of the medium-opposed surface, namely, a magnetic field for recordation, in the thin film magnetic head.
In general, when a flat upper surface is defined on the upper magnetic pole, the aforementioned non-magnetic auxiliary layer inevitably generates the thinner film portion in the upper magnetic pole. Magnetic saturation tends to occur at the thinner film portion in the upper magnetic pole. If the neck height is set smaller or shorter than the gap depth in the aforementioned manner, magnetic saturation can be suppressed at the thinner film portion to the utmost.
In this case, it is preferable to set the difference between the gap depth and the neck height in a range within 1.0 xcexcm. If the difference between the gap depth and the neck height exceeds 1.0 xcexcm, a magnetic flux tends to disperse in the upper magnetic pole over a region defined by the gap depth. It thus becomes difficult to reliably enhance a magnetic field leaked out of the medium-opposed surface, namely, a magnetic field for recordation, in the thin film magnetic head.
According to a second aspect of the present invention, there is provided a thin film magnetic head comprising: a lower magnetic pole layer extending rearward from a front end exposed at a medium-opposed surface and defining a flat upper surface; a non-magnetic auxiliary layer designed to swell from the flat upper surface of the lower magnetic pole layer at a position retracted from the medium-opposed surface; a non-magnetic gap layer extending over the flat upper surface of the lower magnetic pole layer by a constant thickness at least in a range between the medium-opposed surface and the non-magnetic auxiliary layer; an upper magnetic tip pole piece extending over the non-magnetic gap layer by a predetermined thickness at least in a range defined as a gap depth, said upper magnetic tip pole piece defining a thinner film portion of a reduced thickness smaller than the predetermined thickness on the non-magnetic auxiliary layer; and an upper magnetic pole layer extending from a central position of a coil pattern and received on the upper magnetic tip pole piece at a tip end, wherein a neck height of the upper magnetic tip pole piece is set smaller than the gap depth.
The upper magnetic tip pole piece can be formed on a flat surface in the thin film magnetic head prior to formation of a conductive swirly coil pattern. The core width of the upper magnetic tip pole piece can sufficiently be reduced so as to define a narrower recording track over a magnetic recording medium. In addition, since the neck height is set smaller or shorter than the gap depth, the upper magnetic tip pole piece is allowed to suffer from less magnetic saturation at the thinner film portion as compared with the case where the neck height is set larger than the gap depth. A sufficient quantity of a magnetic flux can be introduced into the front end of the upper magnetic tip pole piece through the thinner film portion. It is possible to reliably enhance a magnetic field leaked out of the medium-opposed surface, namely, a magnetic field for recordation, in the thin film magnetic head.
A flat upper surface may be defined on the upper magnetic tip pole piece in the aforementioned manner. In this case, the difference between the gap depth and the neck height should be set smaller than 1.0 xcexcm, as described above.
The upper magnetic pole layer may be terminated at a position retracted from the medium-opposed surface by a distance larger than the neck height in the thin film magnetic head. Even if the upper magnetic pole layer is terminated before it reaches the medium-opposed surface in this manner, a magnetic saturation can be suppressed at the thinner film portion of the upper magnetic tip pole piece, as described above. Moreover, the distance may be set smaller than the gap depth. When the upper magnetic pole layer is allowed to reach a position forward of the rear end of a region determined by the gap depth in this manner, the upper magnetic tip pole piece can receive a larger quantity of a magnetic flux from the upper magnetic pole layer.